Hi,
Is this Rhino 4 or 5? There was a meshing problem in Rhino 4 with triangular shaped surfaces or holes, the holes appeared to be closed in shaded mode because of a display mesh bug. They look correct in wireframe mode.
This bug should have been fixed in Rhino 5. To fix in Rhino 4, you will have to go into the display mesh settings for the file and create a custom mesh setting that has “simple planes” unchecked
–Mitch
The global mesh settings for the document are in DocumentProperties > Mesh page, For individual objects, you can override the global settings in the object Properies, Custom Mesh.